a) Field of the invention
This invention relates to methods of controlling distance between members during article manufacture and in particular it relates to a method of making magnetic device cores.
b) Discussion of Prior Art
In certain industries where extreme minimal manufacturing tolerances are required, it is sometimes necessary to provide gaps of minimal dimensions, e.g. below 3 mil, with negligible dimensional error. Such small gaps may be required in the manufacture of for instance, magnetic device cores, capacitors or in the optical industry. In the case of magnetic device cores (e.g. as used in transformers and inductors), these comprise two axially aligned core halves formed of a material having a magnetic property, the core halves surrounding a wound magnetic core with each core half providing a radially extending core end at an associated end of the core. In this construction, each core half has at least two axially extending elements which extend from the radial core end of the core half. The first of these elements of the two core halves are axially aligned from one core half to the other and extend towards each other within a passage defined centrally of the wound magnetic coil. The second elements of the two core halves are axially aligned from one core half to the other and extend towards each other in positions outwardly of the wound magnetic coil to provide an axial space of determined size between the second elements. The distance apart of the second elements is determined so as to control the distance apart of the first elements within the wound magnetic coil so as to provide the finished product with required magnetic and electrical characteristics. Normally, the gap between the first elements is controlled by providing a specific axial length to each core half and upon assembly of the core, the core halves are disposed axially together with a non-conductive spacer of known thickness between the second elements of the core halves on the outside of the coil. The core halves are then clamped together with a magnetic coil disposed therein and the spacer with the clamps in position determines the space between the second elements and thus determines the distance between the first elements, i.e. across the gap between their confronting ends within the coil.
Problems exist however with the above conventional method of making the assembly. Spacers disposed between the core halves, which may be of Mylar.TM. or other materials are particularly difficult to locate and to hold in position between the second elements during the assembly process. Misalignment of spacers may then result. Alternatively, the spacer material may become creased thereby resulting in incorrect spacing apart of the second elements and thus of the first elements with consequent performance deviations in the finished magnetic device core. The misalignment of a spacer between the second elements may be to such a degree that the whole of the spacer is not located between the second elements. In addition, the present manufacturing processes realistically achieve air gaps between the first elements only as low as 1 mil dependent upon the thickness of the spacer material. Further to the use of spacers between the second elements, grinding of one of the ends of the first elements may be a part of the manufacturing process for determination of the air gap. However, when the grinding step is employed, the minimum air gap which may be achieved is of the order of 3 mil.
Clearly therefore with the known methods of assembly of magnetic device cores, the achievement of minimum gaps of 1 mil to 3 mil places a restriction on the minimum producible size a magnetic device core may achieve. It would be in the interest of present technology, for instance, for the use of magnetic device cores upon printed circuit boards, if such cores could be made of a suitable small size. It would also be of interest to be able to provide extremely small gaps of accurately controlled size between elements of a product generally.